In the related art, methods are known whereby logs are observed visually or optically in order to sort them according to their quality. In a method based on visual inspection, the person performing the sorting directs the logs to different piles on the basis of visual observation. However, this method does not reveal the internal properties of the logs. In optical measurement of dimensions, the measurement is taken from the surface of the bark, which means that variations in bark thickness may result in considerable errors in the determination of the dimensions and volume of the log. These methods for the inspection of logs are mainly focused on measuring log thickness, and the measurement data is communicated to a sorter, who directs the logs manually to appropriate piles according to this information. These methods generally provide no other information about the logs. According to investigations, another drawback is that when the sorting is done by a human sorter, only about half of the logs are sorted fairly correctly with regard to the desired result.
A further drawback with the above methods is that, even if metal detectors are used, it is not possible to identify all foreign objects, such as rocks and non-ferrous metals, that may be present in the logs. Therefore, such objects remain inside the log and may cause damage in the equipment used for further processing of the logs. Finnish patent application no. FI893938 (corresponding to U.S. Pat. No. 5,023,805) presents a method based on three-projection X-ray photography, known in itself in prior art. In this method, from each radiographic projection, the knot terminations are first determined via a longitudinal reconstruction of the log, whereupon knot vectors matching these points are calculated. The weakness of this method consists in the fact that the terminations cannot be determined sufficiently accurately and unambiguously from real logs. Among the reasons for this are overlapping knots and the moisture of fresh wood, which obliterates parts of the knot. Accordingly, what is needed is a method for determining the properties of a moving object such as a log such that the aforementioned drawbacks can be avoided or eliminated.
The object of the present invention is to eliminate the drawbacks of the methods described above and to achieve a reliable and effective method for determining the properties of logs relating to their quality. The method involves using knowledge relating to the geometry, density and other properties of the moving object, as well as inter-dependency between the properties, to allow sorting according to quality.
The operation, measuring and data processing performed by equipment of the invention is based on wood-related knowledge defined by wood quality, and on radiological application of this knowledge. The method comprises a radiological, adaptive expert system based on a knowledge of wood. The procedure can also be applied to other objects or materials moved as bulk goods.
The method has the advantage that it enables the internal defects of bulk goods moving on a conveyor line to be measured and identified using only few projections. This allows reliable determination of quality properties of logs moving at sawing speed. The measurements of the log can also be taken from the log surface beneath the bark, so that the true dimensions of the wooden part of the log can be accurately measured. Instead of using knot outlines in the pictures in a longitudinal reconstruction of the log, as in the above-mentioned patent specification, the method in accordance with the present invention employs the principles of fuzzy logic to locate, by means of a reconstruction formed in a direction perpendicular to the longitudinal axis and utilizing layered slices, three-dimensional objects in which the knot mass is concentrated.
The procedure can be used to determine internal and external properties of logs. The external properties include log length, diameter, conicity and ellipticity as well as bends, multiple crookedness, crooked-growth and volume. One of the advantages of the invention is that the diameter, conicity and volume measurements can be determined from a log with the bark on it for the log without bark. Thus, accurate measurements of the useful wood portion are obtained.
Internal defects of the log include resin pockets, rotten spots, cavities and clefts and also foreign objects, such as rocks and ferrous and other metals. The procedure provides thorough and reliable information about the knots and knot clusters as well as their quality inside the log. The procedure also reveals variations in density and moisture of the wood. By sorting the logs by quality as provided by the invention, healthy knots, dry and rotten areas and their transition zones can be determined.
An important feature regarding measurement and costs is a fast log analysis achieved at a relatively low cost. It is possible to increase both the intensity of X-ray radiation and the computing power to produce a faster analysis, but this could lead to excessive additional costs. In the accordance with an embodiment of the invention, both the intensity of X-ray radiation and the computing power are optimized and to attain the desired speed and accuracy at a relatively low cost. One of the factors contributing to this is that the amount of measurement data can be significantly reduced as compared with prior-art solutions.